The present invention relates to an electric alternator or generator, having a compact size and improved bearing support properties, and improved cooling characteristics.
Electric motors or alternators (dynamoelectric machines) having a stator secured within the housing of the machine and a rotor assembly that extends axially through the motor or generator are well known. Air cooling is typically provided by a centrifugal fan attached to the rotor assembly. Support bearings for the rotor assembly are typically positioned xe2x80x9cinboardxe2x80x9d of the pulley that turns the rotor of the generator via a fan belt from the engine, the pulley also being attached to the rotor assembly. Such devices desirably put as little stress as possible on the bearings that support the rotor assembly, to reduce the torque required to turn the rotors and to prolong the life of the bearings and the pulley. Conventional arrangements subject the bearings to a cantilever force from the fan belt. It is therefore one objective of the present invention to provide a motor with a design that minimizes the stress on the bearings.
Electric machines of this type are typically designed to fit into tight spaces, and therefore desirably are made as compact as possible. It is therefore another objective of the present invention to provide a design that results in a compact machine.
In order to achieve the foregoing objectives the overall layout and design of the present invention produces a smaller size while also providing reduced pulley and bearing stress. The invention accomplishes this objective through an internal, single fan design and a new arrangement of the front bearings and pulley, locating the front bearings outboard of the pulley, which shortens the length of the machine. An electric motor or generator built according to the present invention comprises a drive end frame assembly and slip ring frame assembly that house a stator assembly, a rotor assembly, a rectifier assembly, and a brush-holder/regulator assembly. Cooling air is pulled axially through the machine by an internal centrifugal fan located towards the front of the housing. Through an innovative frame assembly and stack up design, no wall is present between the fan and the pulley, as is typically the case in conventional designs. The removal of the wall reduces the overall length of the generator and allows the outer diameter of the fan to be as large as the outer diameter of the stator. The increased diameter of the fan significantly increase the airflow generated by the fan, resulting in at least two benefits: the cooling capacity of the single fan is substantially increased; and the higher exhaust velocity increases the amount of cooling air that is recirculated through the unit. The air exhausts through scroll diffuser vanes which increase the exhaust flow rates while maintaining the safety of an internal fan arrangement. The increased flow capacity of the invention results in cooler operating temperatures, increased electrical output and longer lasting equipment.
The bearings of the present invention that support the rotor shaft are located on each outside end of the rotor shaft. The front bearing that supports the rotor shaft is installed outboard of the pulley, significantly lowering the load on the bearings and the rotor shaft by eliminating or significantly reducing the cantilever force from the drive belt. The pulley is sandwiched between the bearing and a housing segment, and transmits torque to the rotor shaft through use of multiple spines that engage form-fit apertures on the inside diameter of the pulley. Unlike many conventional designs, no axial clamping nut is necessary in the present invention. This design allows the use of plastic pulleys, reducing manufacturing costs and weight. The compact nature of this design make it possible to install this invention in smaller spaces than conventional designs.